1. Field of the Invention
The present invention relates to an AFC (Automatic Frequency Control) of a QPSK (Quadrature Phase Shift Keying) modulation system, and more particularly to an AFC device and method of a QPSK modulation system capable of raising an accuracy of the AFC by calculating a frequency difference excluding an error symbol.
2. Background of the Related Art
In general, when a channel is changed in a mobile communication system, a transmission/reception frequency is also changed. Thus, a receiving side needs to be tuned with the corresponding changed frequency used by the sending side.
Further, the receiving side uses an AFC device to detect an allocated channel frequency. In addition, the receiving side also uses the AFC device to prevent degradation of the receive sensitivity due to a multi-path fading phenomenon.
A general AFC device calculates frequency differences between adjacent I and Q signals using a frequency discriminator of a cross product type, calculates an average value of the calculated frequency differences, and then performs AFC using the obtained average value.
In this manner, the general AFC device calculates the frequency difference using a symbol of a received training sequence and performs AFC using the calculated frequency difference. However, the general AFC device calculates a frequency difference of the training sequence including an error symbol, which reduces the accuracy of the frequency difference value and degrades the performance of the AFC device.